Soap bars for cleaning use are typically prepared by neutralizing fatty acids with an aqueous solution of a base such as sodium hydroxide, potassium hydroxide, or an alkanolamine. The fatty acids are typically derived from natural sources, such as beef tallow, mutton tallow, palm oil, olive oil, palm kernel oil, and coconut oil, among others. These natural sources contain fatty acid components which are predominantly of even chain length due to the biochemical synthesis mechanism of living organisms.
Commercial soap bars are produced from blends of naturally derived fatty acids chosen to optimize specific performance characteristics. A soap formed from lower molecular weight saturated fatty acids in the range of about 8 to 12 carbon atoms produces a bar which rapidly generates large quantities of bubbles which quickly break on continued lathering. Higher molecular weight saturated fatty acids in the 14 to 18 carbon range produce soap bars which slowly generate a dense, creamy, stable foam on lathering. A bar produced from predominantly short chain fatty acid soaps has a relatively short lifetime because the soap dissolves rapidly in water. Conversely, long chain saturated fatty acid soaps are relatively less soluble and a bar produced therefrom has a longer lifetime. Unsaturated fatty acid soaps such as are produced from oleic acid are more soluble than the saturated long chain soaps and also tend to develop lather faster. However, the foam generated is dense and creamy, and is thus similar in this respect to the long chain saturated soaps.
To obtain a balance of the properties of fast foam generation (flash foam), good foam volume, rich and creamy lather, and acceptable bar lifetime, commercial soap manufacturers typically employ a fatty acid blend comprised of about 80% tallow fatty acid and about 20% coconut-type fatty acid. Specifications for a typical tallow fatty acid and coconut-type fatty acid are listed in the table below.
TABLE 1 ______________________________________ TYPICAL COMPOSITION BY CHAIN LENGTH Chain Tallow Coconut-Type Length Fatty Acid Fatty Acid ______________________________________ C.sub.8 -- 7.0 C.sub.9 -- -- C.sub.10 -- 6.0 C.sub.12 -- 51.0 C.sub.14 2.5 18.0 C.sub.15 0.5 -- C.sub.16 27.0 10.0 C.sub.16:1 4.0 -- C.sub.17 1.0 -- C.sub.18 17.0 7.0 C.sub.18:1 42.0 1.0 C.sub.18:2 5.0 -- C.sub.18:2 5.0 -- C.sub.18:3 1.0 -- ______________________________________
Typically, a formulator attempting to improve one property of a bar will have to sacrifice a portion of the performance of another property. Without incorporation of specific soap additives to alter bar properties, a shifting of the component fatty acid composition to a higher long chain saturated acid content will produce a bar with improved lather richness but will result in a loss of a portion of the flash foam and foam volume properties. Shifting the composition to a higher short chain saturated acid content will produce a bar having improved flash foam but with diminished lather richness and a decreased lifetime of the bar.